Wishlist Screen

// 1) Home / product list – flip the flag in the list we already have
fun toggleWishlist(productId: Int) {
    viewModelScope.launch {
        when (val r = repo.toggleWishlist(productId)) {
            is Result.Success -> {
                _state.value = _state.value.copy(items = _state.value.items.withWishlist(productId, r.data.inWishlist))
                _messages.emit(r.message)               // "Added to wishlist."
            }
            is Result.Error -> _messages.emit(r.message)
        }
    }
}

// 2) Product detail – update the detail object and the toolbar heart
_state.value = UiState.Success(cur.copy(inWishlist = r.data.inWishlist))

// 3) Wishlist screen – a heart tap always means "remove" (see WishlistFragment.kt)

package com.codingeasily.karteasy.ui.product

import com.codingeasily.karteasy.data.model.Product

/** After a heart tap, return the same list with that product's in_wishlist flipped. */
fun List<Product>.withWishlist(productId: Int, inWishlist: Boolean): List<Product> =
    map { if (it.id == productId) it.copy(inWishlist = inWishlist) else it }

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/list"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:clipToPadding="false"
        android:padding="8dp"
        tools:listitem="@layout/item_product" />

    <include
        android:id="@+id/state"
        layout="@layout/layout_state" />
</FrameLayout>

package com.codingeasily.karteasy.ui.wishlist

import android.app.Application
import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.core.os.bundleOf
import androidx.fragment.app.Fragment
import androidx.fragment.app.viewModels
import androidx.lifecycle.AndroidViewModel
import androidx.lifecycle.viewModelScope
import androidx.navigation.fragment.findNavController
import androidx.recyclerview.widget.GridLayoutManager
import com.codingeasily.karteasy.R
import com.codingeasily.karteasy.data.api.Result
import com.codingeasily.karteasy.data.api.UiState
import com.codingeasily.karteasy.data.model.Product
import com.codingeasily.karteasy.databinding.FragmentWishlistBinding
import com.codingeasily.karteasy.ui.product.ProductAdapter
import com.codingeasily.karteasy.ui.product.ProductDetailFragment
import com.codingeasily.karteasy.util.collectWhenStarted
import com.codingeasily.karteasy.util.done
import com.codingeasily.karteasy.util.empty
import com.codingeasily.karteasy.util.error
import com.codingeasily.karteasy.util.kartApp
import com.codingeasily.karteasy.util.loading
import com.codingeasily.karteasy.util.snack
import kotlinx.coroutines.flow.MutableSharedFlow
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.SharedFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.launch

class WishlistViewModel(app: Application) : AndroidViewModel(app) {
    private val repo = app.kartApp.repository
    private val _state = MutableStateFlow<UiState<List<Product>>>(UiState.Loading)
    val state: StateFlow<UiState<List<Product>>> = _state
    private val _messages = MutableSharedFlow<String>()
    val messages: SharedFlow<String> = _messages

    fun load() {
        viewModelScope.launch {
            if (_state.value !is UiState.Success) _state.value = UiState.Loading
            _state.value = when (val r = repo.wishlist()) {
                is Result.Success -> UiState.Success(r.data)
                is Result.Error -> UiState.Error(r.message)
            }
        }
    }

    /** In the wishlist a heart tap always means "remove". */
    fun remove(p: Product) {
        val cur = (_state.value as? UiState.Success)?.data ?: return
        _state.value = UiState.Success(cur.filter { it.id != p.id })   // optimistic: hide at once
        viewModelScope.launch {
            val r = repo.toggleWishlist(p.id)
            if (r is Result.Error) { _messages.emit(r.message); load() } else _messages.emit((r as Result.Success).message)
        }
    }

    fun moveToCart(p: Product) {
        viewModelScope.launch {
            when (val r = repo.addToCart(p.id)) {
                is Result.Success -> { repo.toggleWishlist(p.id); _messages.emit("Moved to cart."); load() }
                is Result.Error -> _messages.emit(r.message)
            }
        }
    }
}

class WishlistFragment : Fragment() {

    private var _binding: FragmentWishlistBinding? = null
    private val binding get() = _binding!!
    private val vm: WishlistViewModel by viewModels()

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {
        _binding = FragmentWishlistBinding.inflate(inflater, container, false)
        return binding.root
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        val adapter = ProductAdapter(
            onClick = { findNavController().navigate(R.id.productDetailFragment, bundleOf(ProductDetailFragment.ARG_PRODUCT_ID to it.id)) },
            onWishlist = { vm.remove(it) },
            onAddToCart = { vm.moveToCart(it) }
        )
        binding.list.layoutManager = GridLayoutManager(requireContext(), resources.getInteger(R.integer.product_columns))
        binding.list.adapter = adapter

        collectWhenStarted(vm.state) { state ->
            when (state) {
                is UiState.Loading -> binding.state.loading()
                is UiState.Error -> binding.state.error(state.message) { vm.load() }
                is UiState.Success -> {
                    adapter.submitList(state.data)
                    if (state.data.isEmpty()) binding.state.empty(R.drawable.ic_heart_outline, R.string.wishlist_empty, R.string.start_shopping) {
                        findNavController().navigate(R.id.homeFragment)
                    } else binding.state.done()
                }
            }
        }
        collectWhenStarted(vm.messages) { snack(it) }
    }

    override fun onResume() {
        super.onResume()
        vm.load()
    }

    override fun onDestroyView() {
        super.onDestroyView()
        _binding = null
    }
}

// CartViewModel.kt – "Save for later" moves an item from the cart to the wishlist
fun moveToWishlist(item: CartItem) {
    viewModelScope.launch {
        val r = repo.toggleWishlist(item.productId)
        if (r is Result.Success && !r.data.inWishlist) repo.toggleWishlist(item.productId) // was already there
        update { repo.removeFromCart(item.productId) }
        _messages.emit("Moved to wishlist.")
    }
}